BEHAVIORAL AND EEG CHANGES IN SHEEP IN RESPONSE TO PAINFUL ACUTE ELECTRICAL STIMULI

Objective To measure acute pain in sheep, based on a human pain model, and examined changes in both electroencephalogram frequency spectrum and behavioural responses to increased electrical stimulation in sheep . Design Analysis of variance (treatment and animal effects) for stimu lus intensity where each animal received each electric shock treatment given in the order 0, 5, 10 and 20 mA. Procedure Eight sheep with ele ctrodes implanted over the surface of the brain were examined for esca pe-avoidance and electroencephalogram responses to four levels of elec trical stimulation from 0-20 mA. Results With increasing stimulus inte nsity at the time of feeding, the sheep were more hesitant to return t o the feeder or remain near the feeder following stimulation. There wa s little difference between the 0 and 5 mA stimuli for any of the beha viour variables (P > 0.05). However, there were marked increases in th e time taken to re-approach the feeder after receiving an electric sho ck of 5 mA and of 20 mA (P < 0.05; mean values 3 and 119 s, respective ly) and remaining near the feeder for 5 s (P < 0.001; mean values 10 a nd 167 s, respectively). Following the stimulus, there was an overall increase in the electroencephalogram power spectrum in the first four seconds, which then rapidly returned to normal. In particular, the 20 mA stimulus resulted in higher absolute power values than in the contr ol (0 mA) treatment for delta 2 (P < 0.001), theta 1 (P < 0.05), theta 2 (P < 0.05), alpha 1 (P < 0.001), alpha 2 (P < 0.001) and beta 1 (P < 0.01) bandwidths. Similarly, for the 10 mA stimulus, the absolute po wer values were greater than the control treatment for delta 2 (P < 0. 05), alpha 1 (P < 0.01), alpha 2 (P < 0.001) and beta 1 (P < 0.01) ban dwidths. Conclusion The experiment suggests that a human acute pain mo del is applicable to sheep and that these electroencephalogram changes may provide a good measure of acute pain in sheep.